Marine pollutions due to petroleum spill, for example, the oil spill from the Gulf War in 1991 and the oil spill in the Gulf of Mexico in 2010, are continuing to cause environmental damage. This is because hazardous components such as an aromatic compound contained in the crude oil released in water are diffused and inflict extensive damage to living organisms.
Therefore, if by any chance such spill is caused, there is a need to rapidly recover the oil before it is carried away by the ocean current and diffuses.
Conventional methods for recovering oil that leaked into the ocean, rivers, lakes and the like have owed to oil adsorptive storage, recovery through gelation, or a combination thereof.
Specifically, adsorptive storage refers to recovery by trapping the oil in the gap between fiber or microparticles.
Conventionally, layers of non-woven fabric made from natural fiber or synthetic fiber (Patent Document 1), urethane foam or fine-grained mineral (calcined and foamed) (Patent Document 2) have been widely used.
Gelation refers to a recovery method in which the oil is gelated using resin acids or metallic soaps such as metallic salts of rosins (Patent Document 3). In addition, oil-adsorbing materials that use a polynorbornene resin or a styrene-butadiene copolymer have also been developed (Patent Document 4).
According to the recovery method by adsorptively storing the oil in the gap in non-woven fabric or foam, however, water may as well be absorbed simultaneously with the oil, which may impair the absorption efficiency. Moreover, since the force for retaining the absorbed oil is low, there is also a problem that the absorbed oil may ooze and be released due to external pressure applied during transportation for recovery.
Although oil recovery by a method of gelating the oil is effective since it allows the oil to be selectively absorbed, it has a problem in that a raw material of the oil-adsorbing material, i.e., a resin such as polynorbornene, is expensive. Furthermore, since degradation of the resin can be caused during storing, for example, an additive for preventing such degradation needs to be added, resulting in a problem of high cost. Additionally, since gelation, which is effective in the case of a small amount of leakage, requires stirring, it is unsuitable when a large amount of oil needs to be recovered, for example, upon a crude oil spill incident.
Moreover, although an oil dispersant was used for handling unrecovered crude oil upon a major incident like the oil spill in the Gulf of Mexico in 2010, since an oil dispersant is made of a surfactant and an organic solvent, the adverse influences of the dispersed components on the ecological system are currently still posing a problem.
Meanwhile, Patent Documents 5-7 describe a polycarbonate diol and a carbonate system compound similar to the material focused by the present inventors, but they do not describe about a purpose or an application for oil recovery and thus completely lack description about the oil absorption. Furthermore, the molecular weights of these polymers are all as low as 10,000 or less.